A trailer is a great idea. You can even leave it packed if you have a good secure place to store it. I would like to have one like in your pic, perfect size!
As for a vehicle for your needs, you could get a used something as a wilderness thrasher. I bought an Isuzu Trooper with lots of space, decent off road performance and sort of expendable. It does not get the best of milage on the highway though. About 20 MPG tops.
As for bugging out of PHX, I doubt any of us will get far in a crisis. It took 2 hours to get 20 miles on I-17 last night and that was without any accidents to tie things up. Just the usual on a Sunday night heading back to the city. Imagine if everyone were trying to leave the city at the same time, you would not get anywhere except stuck in your vehicle. A good plane would be really handy to own!! A Beaver would be perfect. Maybe someday I will be rich:)